Everyone always forgets the 70-300mm DO IS.
I had one of these and it was a really great lens. It is tiny, about the same size as a 17-55mm, great range and fairly quick for a zoom.
There will always be people that talk about the halo effect but it didn't bother me at all and is only really noticeable when pixel peeping. If its a travel lens for the size you will find it hard to beat. The white Ls are awesome and I swapped mine for a 70-200mm but its huge and heavy and over the top if you are traveling.
I would say have a look see what you think. I wish I never sold mine.
That is an important aspect! Did you swap to the new USM II? If so have you noticed IQ differences compared to the 70-300?
The 70-300mm DO IS is not an L lens. But it is about half the size of the 70-300mm L IS. The 70-300mm DO is USM but not II and has the first gen IS so 2 stops. Obviously the IQ of the L is better but it is heavier and a lot bigger. Also stands out like a sore thumb.
But it is a compromise, if you want something small lightweight and inconspicuous then it fits the bill. If you want ultimate lens the 28-300mm although it is very very heavy very expensive and a complete pain if you ask me. 70-300mm L is also a great lens but is big and also stands out. Would be a pain to carry around.
The DO gives good IQ although does have the halo effect, has IS is USM and is the same size as a standard zoom. Good compromise but obviously not for everyone.
The 70-300mm DO is the one on the right! next to the 75-300mm (non L) and the 100-400mm Its so small! Also comes with a hood.
If I was going traveling with the 7D I would take a 17-55mm IS, 70-300mm DO IS, possibly the 10-22mm or a 35mm.
Some more info.http://www.the-digital-picture.com/Reviews/Canon-EF-70-300mm-f-4.5-5.6-DO-IS-USM-Lens-Review.aspx
Obviously highlights the problems but I have taken some great shots with mine when I had it. You can get them pre-owned for around £500 in perfect condition.